Air-cooled Generators Having Competitive Performances to Conventional H_2-cooled Machines

摘要

Generator design has achieved marked advancement in recent years due to corollary innovations made in modern tool design concepts. In addition to their basic electrical requirements, these new technologies also require improved loss distribution, better ventilation, lower temperatures and better vibration control. Mechanical and electrical losses coupled with vibration are inherent in two-pole commercial turbine generators that rotate at 3000 or 3600 rpm. Highly accurate tool designs are absolutely required for such applications. To produce high quality generators, it is essential to be able to accurately calculate the core losses, stray load losses, and temperature variations. With air-cooled generators, the issue of mechanical loss also arises. Compared with hydrogen-cooled generators, air-cooled generators are easy to handle; but the drawbacks are larger mechanical losses, a higher temperature rise, and larger dimensions. To develop air-cooled generators that are lightweight, highly efficient, and that operate at lower temperatures, we have studied all of the design parameters and have calculated factorial effects on performance. The first step was lowering and averaging of the rotor and stator temperatures. Adopting the Taguchi Method (robust design) gave us an introduction to obtain lower ventilation and smaller rotor diameter, both of which drastically reduced mechanical loss. The next approach was to reduce core loss and stray load loss. A study into iron loss in the stator core structure suggested that pure iron loss, in other words, loss generated in the core lamination sheet, may not be dominant, but that other surrounding structures, including supports, sometimes account for a significant part of the total iron loss. Therefore, after choosing the core material, the surrounding structure was designed to have minimum additional loss. The stray load loss was also studied and minimized. Accordingly, the factorial effect of every performance was studied, and by choosing the optimal combination of design parameters, we were able to minimize temperature rise, weight, and loss. The technology of air-cooled generators has reached a state-of-the-art level. The lightest, coolest, and most efficient 160-MVA generator with 98.75% efficiency is now completed.